Select which GPUs to use for rendering
Yes, when you have more than 1 GPU blender options are all the GPUs at once and then each single individual GPU.

This feature is on the dev's todo list for longer than 2 years.

You can check it here: https://developer.blender.org/T37717

Dec 8 2013, Brecht wrote:


  It's on my todo list to improve graphics card configuration for 2.70, to allow you to select individual cards and enable/disable them. This is not considered a bug at the moment however.